In recent years, with the emergence of various new types of multimedia electronic products, and with the development of broadband data connections and wired and wireless connection technology for use in a private network, more and more people are connecting their own computing devices together via a private network (for example, a home network) so as to share various resources. For example, people want to be able to share the media content (e.g. movies, music etc.) on various computing devices via their home networks. Meanwhile, to attract more customers, a number of media content providers have removed the binding between media content and specific rendering devices, thereby extending the rendering range of the media content to an authorized domain. This is implemented by substituting the offline and one way authentication-based broadcast encryption method for the traditional online and two way authentication-based public key infrastructure (PKI) method.
For example, when employing the broadcast encryption method to protect the media content on a physical media, each media has a data block thereon referred to as a key management block (KMB), while each trusted computing device (e.g. a trusted media player), for rendering the media content on a physical media, will first read the KMB and generate a key for reading the media content on the physical media by processing the KMB. That key is referred to as a management key. The computing device that can generate the correct management key can render the media content on the physical media. Thus, the binding between media content and a specific rendering device is removed through the broadcast encryption, thereby extending the rendering range of the media content to a set of computing devices which can generate the correct management key by processing the KMB on the media. Such a set of computing devices constitute an authorized domain. Within the authorized domain, each trusted computing device could share the media content equally or peer-to-peer, that is: the media content can flow from any one of the computing devices to another computing device. Although this provides legality for the sharing of media content in a private network, there still are many technical problems to be resolved.
First, various computing devices on a private network, such as PC, set-top box, FDA and mobile phone etc., have different system capabilities and media features. Most low-end computing devices such as set-top hoses, PDAs and mobile phones etc. do not have enough storage, for storing large media file in local storage, and need media streaming technology to render the media content that resides on larger computing devices, such as PC and home media server. And also, by relying on media streaming technology, it is possible to implement peer-to-peer media content sharing among various low-end computing devices.
At present, many standard organizations have defined a variety of secure media streaming solutions, but they all have limitations and could not be used in sharing media content in a private network. For example, Internet Media Streaming Alliance (ISMA) has presented an ISMA 1.0 implementation specification to promote the existing IETF and MPEG standards for broadcasting via Internet. It is said that the publication of the specification is helpful to generate a complete, open and peer-to-peer multimedia streaming solution used in an IP network. In that specification, ISMA has defined two layers. First, layer 0 focuses on rendering audio/video content to low-complexity devices via wireless and narrowband networks, low-complexity devices including devices such as cell phones and PDAs which limit the viewing and listening performance. Next, layer 1 focuses on rendering content via a network, that has broadband-like quality so as to provide more abundant viewing experience for end users. Layer 1 is oriented to devices with more powerful functions, such as set-top boxes and PCs. ISMA 1.0 employs MPEG-4 compression standard and has precisely defined some features of the MPEG-4 standard to ensure interoperability between the entire rendering flow, while these features are necessary to server, client and intermediate part. Also, ISMA 1.0 has defined the features and selected formats of the RTP, RTSP and SDP standards that have to be implemented. Thus it can be seen that ISMA 1.0 is a new media streaming specification, proposed as a standard for Internet streaming infrastructure. It could not be deployed on existing private networks that use a diversity of transport protocols and media formats.
In addition, the present media streaming technology all works in client/server mode, hence a powerful media streaming server is needed.
This kind of working mode is not suitable for sharing media content in a private network. The sharing of media content in a private network should employ a peer-to-peer working mode to ensure that the media content can flow from any computing device to any other computing device in the private network. Also, the typical computing device in a private network only has limited system resources and could not act as a media streaming server.
To share media content in a private network, another problem to be solved is how to implement a media streaming solution that is independent of media format, so that each computing device on the private network can share the media content. For example, Windows, Apple QuickTime and Realnetwork media streaming solutions all support a restricted number of media formats. Thus, the problem of sharing media content peer-to-peer in a private network could not be solved by installing the above server and client program on all the computing devices in the private network simultaneously. Also adaptation issues for other customized private formats and new schemes that may appear in the future will exist.